In recent years, radiation transfer systems have been developed to obtain prints from pictures which have been generated electronically from a color video camera; to obtain a color proof image before a printing press run is made; to form patterns on substrates for electronic, optical, and magnetic devices; and to form color filter arrays.
According to one way of obtaining prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face and in contact with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta or yellow signal. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are contained in commonly assigned U.S. Pat. No. 4,621,271, the teaching of which is hereby incorporated by reference. A method for reduction of donor utilization in this contact thermal printing method is described in U.S. Pat. No. 5,555,102, the disclosure of which is incorporated herein by reference. Other methods to reduce donor utilization in dye diffusion printing are known in the art, and include the use of differential donor to receiver speeds. The problem with these methods is that in dye diffusion printing there is contact between the donor and receiver, which results in high frictional forces acting on the donor in the printhead location. This can result in poor density control, donor wrinkling and tearing.